where \({X} = \lbrace {Z}\rbrace \)  and \({R} = \lbrace {Z}\rbrace \)  are the reactance and radiation components, respectively, of impedance matrix \({Z}\)  evaluated via a method-of-moments formulation of the electric field integral equationFormula (REF ) can be applied for other formulations as well, identifying proper reactance and radiating operators [1]}. [2]}, \({I}_n\)  are vectors of expansion coefficients representing characteristic current densities \(J̭_n\) , and \(\lambda _n\)  are the eigenvalues related to \(t_n\)  via [1]}
\(t_n = -\frac{1}{1 + J\lambda _n}.\) 
